For Beginners!

• My Favorite Beginner's Pixel Art Tutorial
• Top 5 Basic Tips for Pixel Artist
• Final Boss Blue's Pixel Art Tutorials, a good expanded beginner's series of pixel art tutorials.
• How to use AntiAliasing
• How to make clean lines
• Blending colors & shading tips
• How to Pick Nice Colors
• RedRabbit talks about color
• Different Perspectives used in games
• Easy steps to improving your sprite work (note: check out the blog's other stuff on textures too!)
• Three more tips on improving your spritework
• a few more quick tips
• A textures collection

Collections

• Lospec, a huuuuuuuuuuuuge collection of tutorials and palettes for pixel art from around the web!
• Studio Miniboss has a TON of tutorials and I highly suggest them as they cover nearly everything
• RHLpixels has some lovely tutorials, from trees to color palettes to character sprites
• MortMort's video tutorials!
• Brullov's tutorials - You don't need to donate to see things like his water, fire, & clusters tutorials

More Advanced

• a tiny introduction to clusters
• a great talk on banding, clusters, and dithering
• an interesting way to create a color palette
• cyangmou's talks and tutorials are nice and in depth. Check out his stuff on perspective!
• slynerd's stuff is pretty cool
• How different pixel artist use color, and the importance of having neutrals in your palette
• Advice on varying up your character sprites.
• Making Pixel art Brushes for Clip Studio Paint
• Avoiding Color Banding